1. Field of the Invention
The present invention relates to a position sensing device and a lens driving module using the same.
2. Description of the Related Art
With recent technical developments, portable terminals such as mobile phone and personal digital assistant (PDA) are used as multi convergence in music, movie, TV, and game as well as phone call function. One typical technology for the multi convergence is a camera module. A resolution of the camera module is changing from 300,000 pixels (VGA) to more than 7,000,000 pixels. Simultaneously, a variety of functions such as auto focusing (AF) and optical zoom are realized.
In particular, demand for mobile phones having a camera module with the AF function mounted therein is rapidly increasing, because the mobile phones can provide a high-quality image regardless of a focal distance from an object.
In the camera module with the AF function, as a lens barrel having a plurality of lenses stacked therein or the lenses inside the lens barrel is/are vertically driven by an actuator composed of an electromagnetic motor or piezoelectric element, the focus is adjusted regardless of a distance from an object. The actuator is driven by a position sensing device which sets an initial position for accurately performing focus adjustment of the lenses.
FIG. 1 is a perspective view of a conventional position sensing device mounted in a camera module. FIG. 2 is a graph showing a movement distance in accordance with a voltage generated by the conventional position sensing device. As shown in FIG. 1, the conventional position sensing device includes a sensor 1 having a body composed of a light receiving section 2 and a light emitting section 3 facing each other and a light shield 5 inserted between the light receiving section 2 and the light emitting section 3 of the sensor 1.
The sensor 1 is mounted on a side surface of a lens barrel (not shown) or on a barrel driving section through a plurality of holders 4.
In the sensor 1, light emitted from the light emitting section 3 is incident on the light receiving section 2, and the actuator which transfers the lenses is driven by the light incident on the light receiving section 2. At this time, the receiving and shielding of the light received by the receiving section 2 of the sensor 1 is controlled by the light shield 5 which is mounted so as to be vertically transferred between the light receiving section 2 and the light emitting section 3. As the light shield 5 is vertically transferred, portions of the light receiving section 2 and the light emitting section 3 are shielded. At this time, while the light transmitted between the light receiving section 2 and the light emitting section 3 is converted, a voltage is generated. Then, the lens is transferred by the actuator driven by the generated voltage.
At this time, when the lens reaches the initial position, the light shield 5 between the light emitting section 3 and the light receiving section 2 shields the entire area of the light emitting section 3 and the light receiving section 2 such that the light transmitted therebetween is completely shielded. Then, the initial position of the lens in a state where the voltage is not applied can be sensed.
Further, when the light shield 5 between the light emitting section 3 and the light receiving section 2 is transferred upward such that the transmission of light therebetween begins, a predetermined voltage is applied to the actuator for transferring the lens. Then, the actuator is continuously driven.
Therefore, the conventional position sensing device can relatively accurately sense the initial position of the lens. However, in a state where the light shield 5 is positioned in a position between the light emitting section 3 and the light receiving section 2, the position sensing device cannot sense the position of the lens. Therefore, it is difficult to measure how much the actuator should be driven so as to reach the initial position.
Further, when the light shield 5 is positioned in such a manner that the transmission of light between the light emitting section 3 and the light receiving section 2 can be performed, and if the lens is physically transferred to the initial position, the lens may collide with other components such that the lens and the actuator are damaged.
That is, as shown in FIG. 2, only the application of voltage to the actuator for transferring the lens can be grasped through the transmission and shielding of the light by using the light shield 5 between the light receiving section 2 and the light emitting section 3. Therefore, the lens cannot be transferred in a stepwise manner, and the failure rate of the actuator increases due to the rapid transfer of the actuator.